(a) Field of the Invention
The present invention relates to a polyester yarn which can be used in a fabric for an airbag, and more particularly, to a high-strength and low-modulus polyester yarn which has excellent mechanical properties, shape stability, packing property or the like, and a production method thereof, and a fabric for an airbag using the same.
(b) Description of the Related Art
Generally, an airbag is a device for protecting a driver and passengers, in which a crash impact is detected by an impact detecting sensor when driving vehicles collide head-on at a speed of about 40 km/h or higher, and consequently, gunpowder explodes to supply gas into an airbag cushion to inflate the airbag. A general structure of an airbag system is depicted in FIG. 1.
As depicted in FIG. 1, the conventional airbag system includes: an inflator 121 that generates a gas by ignition of a detonator 122; an airbag module 100 that includes an airbag 124 that is expanded and unfolded toward a driver on the driver's seat by the generated gas, and is installed in a steering wheel 101; an impact sensor 130 that gives an impact signal when the vehicle has crashed; and an electronic control module 110 that ignites the detonator 122 of the inflator 121 according to the impact signal. In such airbag system, the impact sensor 130 detects the impact and sends the signal to the electronic control module 110 when the vehicle collides head-on. At this time, the electronic control module 110 that received the signal ignites the detonator 122 and a gas generator in the inflator 121 is combusted. The combusted gas generator rapidly generates the gas to expand the airbag 124. The expanded airbag 124 contacts the front upper body of the driver and partially absorbs the impact load caused by the collision, and when the driver's head and chest go forward according to the law of inertia and smash against the airbag 124, it further absorbs the shock toward the driver by rapidly discharging the gas from the airbag 124 through discharging holes formed on the airbag 124. Therefore, the airbag effectively absorbs the shock that is delivered to the driver at the time of a collision, and can reduce secondary injuries.
As disclosed above, an airbag used in a vehicle is prepared in a certain shape and is installed in the steering wheel, door roof rails, or side pillars of the vehicle in a folded form so as to minimize its volume, and it is expanded and unfolded when the inflator 121 operates.
Therefore, it is very important that the airbag has folding property and flexibility for reducing the shock to the occupant in addition to good mechanical properties of the fabric for effectively maintaining the folding and packaging properties of the airbag when it is installed in a vehicle, preventing damage to and rupture of the airbag itself, providing good unfolding properties of the airbag cushion, and minimizing the impact provided to the occupant. However, an airbag fabric that can maintain superior air-tightness and flexibility for the occupant's safety, sufficiently endure the impact applied to the airbag, and be effectively installed in a vehicle has not yet been suggested.
Previously, a polyamide fiber such as nylon 66 or the like has been used as the raw material of the fiber for an airbag. However, nylon 66 has superior impact resistance but has drawbacks of being inferior to polyester fiber in terms of moisture and heat resistance, light resistance, and shape stability, and being expensive.
Meanwhile, Japanese patent publication No. Hei 04-214437 suggested the use of a polyester fiber for reducing such defects. However, when the airbag was prepared by using the prior polyester yarn, it was difficult to install the airbag in a narrow space in a vehicle because of its high modulus, and there was a limitation for maintaining sufficient mechanical and unfolding properties under severe conditions of high temperature and high humidity.
Therefore, it is needed to develop a fiber yarn that maintains superior shape stability and gas barrier effect so as to be suitably used as a fabric for an airbag, and also maintains flexibility for reducing the impact applied to passengers, the packing property, and superior mechanical properties under severe conditions of high temperature and high humidity.